This invention relates to timed electrical switches, and more particularly to a timed electrical switch for use in a circuit including an auxiliary switching means for controlling the supply of electricity to an electrical load.
An exemplary application of the invention is in an outdoor lighting environment, such as lighting of a sign or billboard. In such a lighting application, it is often desirable to have the billboard illuminated during the times of peak traffic. Such times include the daylight hours, during which artificial illumination is generally unnecessary, as well as a certain number of nighttime hours. For example, the billboard may require illumination from dusk until midnight and from 6:00 a.m. to dawn. It is generally uneconomical to provide illumination from midnight to 6:00 a.m., since traffic is generally low and potential viewers of the billboard too few to justify illumination.
To provide illumination for a billboard according to such a schedule, it is known to use a conventional time switch in combination with a photosensitive switch. However, a photosensitive switch typically is a single-pole switch having a current-carrying capacity much less than that required to power large lighting loads, such as that necessary to illuminate an outdoor billboard. It is also generally the case that such photosensitive controls have a current carrying capacity less than that of a standard double-pole 40 ampere conventional time switch, typically used in such lighting applications. Thus, when controlling large lighting loads, it is necessary to connect the photocontrol so as to control the coil on a relay or contactor. The relay contacts are then sized adequately for the load to be controlled. With such a combination, the photocontrol actuates the coil on the relay or contactor at dusk, thus causing electricity to flow to the lighting to illuminate the billboard. The conventional time switch is typically set to interrupt the supply of electricity at midnight and to restore electricity at 6:00 a.m. At dawn, the photocontrol causes the relay contacts to open, thus turning the lighting off.
A shortcoming of the above-described arrangement is that an auxiliary relay or contactor must be wired into the circuit. Additionally, this configuration provides a duplicity of movable switch contacts for the circuit: one associated with the time switch, and the other associated with the separate relay or contactor.
The present invention is intended to eliminate such shortcomings, and to provide a simple and efficient switching mechanism for lighting and other timed electrical applications. In accordance with the invention, an apparatus for regulating the supply of electricity from an electricity source to an electrical load includes a conventional time switch having a timing mechanism, one or more switch contacts, and switch means responsive to the timing mechanism for selectively connecting and disconnecting the load to and from the electricity source at predetermined times by closing and opening the switch contacts. An auxiliary actuator means, operable independently of the time switch, selectively connects and disconnects the load to and from the power source by closing and opening the same set of switch contacts. The auxiliary actuator means operates in response to an actuator current supplied by a source other than the time switch to provide a supplementary means of connecting the load to the electricity source. In a preferred embodiment, the time switch has one or more switch contacts which are biased toward a closed position. The switch means responsive to the timing mechanism is one or more pivotably mounted cams which, in response to the action of the timing mechanism, bias the contacts away from their normally closed position to open the contacts at predetermined times to disconnect the load from the electricity source. The time switch cams are also responsive to the timing mechanism so as to allow the switch contacts to return to their closed position at a predetermined time in order to reconnect the load to the source. The auxiliary actuator means comprises a solenoid or other electromagnetic device which is movable in response to the flow of a current therethrough. The solenoid is connected to a photosensitive control, which in turn is connected to the electricity source. The photosensitive control allows current to flow from the electricity source to the solenoid in response to detection of an absence of a predetermined level of ambient light in the vicinity of the billboard or other object to be illuminated. The flow of current into the solenoid causes the plunger of the solenoid to withdraw into the cylinder of the solenoid. The plunger of the solenoid is mechanically connected to a linkage, which in turn is mechanically connected to one or more auxiliary switch contact actuating cams which are pivotably mounted alongside the time switch cams. The two sets of cams are movable independently of each other, so that connection of the load to the electricity source can be governed both by the time switch and by the photocontrol via the solenoid. This combination enables an auxiliary photocontrol or other electrical switching means to energize the solenoid, thus closing the switch contacts at a desired point in time, such as dusk. The time switch mechanism then opens the same set of switch contacts according to preselected set times, such as between midnight and 6:00 a.m. At 6:00 a.m., the time switch operates to again close the contacts to reconnect the load. Thereafter, the auxiliary photocontrol cuts off the flow of current to the solenoid at dawn, thus permitting the switch contacts to open to again disconnect the load from the source. This sequence is then repeated at dusk.
The above-referenced construction eliminates the need for a relay or contactor to be wired into the circuit, and also eliminates the separate set of contacts provided by such a mechanism. Actuation of the same set of switch contacts by a time switch and an auxiliary control provides an efficient and compact mechanism for controlling a lighting load.